gui: Added 'empty' mirror alignment tab
XRC Slider scale bug fix
gui: button controls added to align tab (bug present, though)
gui: 'bug' fix for MirrorAlignTab
gui: fixed merge conflict
firststep: gui fix
gui: mirror alignment controls final
gui: fixed PyDeadObjectError
gui: align button face lift
gui: improve metadata display in the acquisition tab

Create a dedicated add_metadata method that knows about each metadata

Use a readonly text entry instead of a label to display readonly text
(the main advantage is that if the text is too long it's just truncated instead
of increasing the size of the window).

Also improve vertical alignment between label and value
Merge branch 'master' of vpn.delmic.com:odemis